1. Field of the Invention
The present invention relates to a radiation detector for detecting radioactive rays and a method for manufacturing the radiation detector.
2. Description of the Related Art
A flat X-ray detector using an active matrix has been developed as a new-generation detector for X-ray diagnosis. Detecting X-rays impinging on the X-ray detector causes an X-ray radiographic image or a real-time X-ray image to be output as digital signals. In the X-ray detector, X-rays are converted to visible light, that is, fluorescence by a scintillation layer, and the fluorescence is converted to signal charges by a photoelectric conversion element, such as an amorphous silicon (a-Si) photodiode or charge coupled device (CCD), so that an image is acquired.
As a material for forming a scintillation layer, in general, cesium iodide (CsI): sodium (Na), cesium iodide (CsI): thallium (Tl), sodium iodide (NaI), gadolinium oxysulfide (Gd2O2S) or the like is used. Upon forming a scintillation layer, a groove is formed by dicing or the like, and a material is deposited by a vapor deposition method so as to form a pillar structure, allowing improvement in resolution characteristics.
To improve sensitivity characteristics by increasing usage efficiency of fluorescence from a scintillation layer, there is a method of forming a reflective film on the scintillation layer. In other words, of fluorescence emitted in the scintillation layer, fluorescence moving toward a side remote from photoelectric conversion elements is reflected from a reflective film to increase fluorescence that arrives at a side of the photoelectric conversion elements.
As an exemplary method of forming a reflective film, a method of forming a metal layer of a silver alloy, aluminum or the like, which has high fluorescence reflectance, on a scintillation layer is generally known. As another method, for example, disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-283483 (pp. 5 to 6, FIG. 1) is a method of applying a reflective material of light-scattering reflective properties, which contains a light-scattering substance, such as TiO2, and binder resin.
A scheme of using a reflective plate having a metal surface of aluminum or the like placed on scintillation layer, instead of a reflective film is also practically implemented.